This relates to heads-up displays such as used for automotive (including trucks, construction machinery, etc.) and other industrial and non-industrial applications.
Heads-up displays (HUDs) are used to present information in the form of virtual images into the field of view (FOV) of a user otherwise engaged in directly observing the outside world or some other primary subject matter. For example, automobile heads-up displays may be used to project instrument panel data or other driving or road condition information onto the windshield of a driver whose primary attention is directed at observing the road ahead. Examples of existing automotive heads-up display systems are given in U.S. Pat. Nos. 4,973,942; 5,061,996; 5,121,099; 5,140,465; 5,731,903; 5,805,119; 6,757,085; 6,789,901; 7,619,825; 7,669,543; and in EP 0 009 332 B1; the entireties of all of which are incorporated herein by reference. Other examples of heads-up display applications include projecting an aiming spot into the field of view of a hunter primarily engaged in looking at a target through a rifle scope, or projecting flight path information onto the canopy of a jet fighter to assist a pilot to land on a deck of an aircraft carrier. A usual objective of such systems is to present information in a manner that can be quickly assimilated without taking attention away from the primary visual objective. The heads-up display apparatus should preferably also be configured to provide minimum obstruction to the view of the outside world and other instruments.
Current HUD designs present a virtual image to the user that is either set at a fixed distance or has a continuously changing focus position due to the virtual image being tilted. There are, however, situations when it is desirable to display two or more virtual images each with a different virtual image distance relative to the viewer. For example, it may be desirable in an automobile heads-up display system to present a first virtual image of symbols, arrows or other directional/warning information far out on the road and a second virtual image of speedometer, temperature, pressure or other instrument panel/sensor data in alphanumeric or analog form beneath the first image at a distance much closer to the viewer. One approach to such multi-focus systems is to use two separate displays set at different locations behind the optics to create spatially separated images at two different virtual image distances. An arrangement of this type is illustrated in FIG. 1.
FIG. 1 illustrates an automobile heads-up display system 100 which projects multiple virtual images 102, 104 at different distances from a driver 106 seated behind a steering wheel and observing the oncoming roadway through a windshield. The far virtual image 102 includes directional/warning information or other graphics that overlay on the road area and is observed ahead of the driver, superimposed over an object of interest down the road. The image 102 may, for example, be a highlighted outline of a road sign and overlapped onto the road sign in order to alert the driver to its presence. The near virtual image 104 includes instrument panel/sensor data and is observed ahead of the driver below the first image and superimposed over the roadway at a position near to the automobile front hood. The image 104 may, for example, be an alphanumerical display of current odometer speed, radiator coolant temperature, oil pressure, and similar data. Both images are presented for viewing in the field of view and provide information to the driver without the need for the driver to look away from the oncoming roadway. In a typical application, the far virtual image may, for example, appear at a distance of somewhere between 8 and 30 meters and the near virtual image may, for example, appear at a distance of somewhere between 2 and 4 meters.
In the illustrated configuration, each image 102, 104 is generated using a different picture generator unit (PGU), such as a respective different LCD panel 108, 110. LCD panel 108 serves as the image display source for far virtual image 102, and LCD panel 110 serves as the image display source for near virtual image 104. The light from each display unit is then directed via a common optical relay path onto the surface of the windshield and then reflected into the driver's field of view. The common optical path may, for example, include first and second mirrors 112, 114 and a light transmitting HUD unit cover 116. The HUD unit LCD panels 108, 110 and optical elements 112, 114 may, for example, be housed in a protected space behind the instrument console with the transparent cover fitted to an opening in the dashboard over the steering wheel. Mirrors 112, 114 may serve reflective and/or folding purposes which together with an image separation distance between the two LCD panels 108, 110 set the different virtual image positions for the two virtual images 102, 104.
Drawbacks to the illustrated arrangement include spatial limitations imposed by dimensional requirements needed for the separate LCD panels, and focus range limitations due to the commonly shared optical components.